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AERIAL NAVIGATION. 



BY 



O. CHANUTE, C.E., 



OF CHICAGO. 



A LECTURE DELIVERED TO THE STUDENTS OF SIBLEY 
COLLEGE, CORNELL UNIVERSITY. 

MAY 24,1890. 



THE RAILROAD AND ENGINEERING JOURNAL, 

145 BROADWAY, NEW YORK. 

189I. 

BURR PRINTING HOUSE, FRANKFORT AND JACOB STS., N. Y. 



AERIAL NAVIGATION. 



BY 



O. CHANUTE, C.E., 



OF CHICAGO. 



A LECTURE DELIVERED TO THE STUDENTS OF SIBLEY 
COLLEGE, CORNELL UNIVERSITY. 



THE RAILROAD AND ENGINEERING JOURNAL, 

145 BROADWAY, NEW YORK. 

I89I. 



TZ.544 



■p. 
397283 
'30 



AERIAL NAVIGATION. 



By O. Chanute, C.E., of Chicago. 



Until quite recent years, the possible solution of the 
last transportation problem remaining for man to evolve — 
that of sailing safely through the air — has been considered 
so nearly impracticable that the mere study of the subject 
was considered as an indication of lunacy. 

And yet such measurable success has recently been 
achieved as to warrant good hopes for the future, and it 
is believed that speeds of 25 to 30 miles per hour, or enough 
to stem a wind less than a brisk gale, are even now in sight. 

This is not unusual in the history of inventions. They 
are first proposed by the men of imagination, the poets 
and the dreamers, and next they are experimented upon by 
the more imaginative inventors, until at last some glimmer 
of success or some powerful incentive induces scientific 
men to investigate the principles, and ingenious inventors 
to endeavor to solve the problem. 

Thus, if we are to believe ancient fable and history, des- 
ultory attempts to fly through the air followed close upon 
the invention of the land chariot and of the marine sail, 
but the mechanical difficulties in the way are so great that 
it is only since light primary motors have been evolved 
that any success at all has been achieved ; and even now 
the students of the problem are divided into two camps or 
schools, each of which expects flight to be compassed by 
somewhat different apparatus. These are : 

1. Aeronauts, who believe that success is to come 
through some form of balloon, and that the apparatus 
must be lighter than the air which it displaces. 

2. Aviators,* who point to the birds, believe that the 
apparatus must be heavier than the air, and hope for suc- 
cess by purely mechanical means. 

Curiously enough, there seems to be very little concert 
of study between these two schools. Each believes the 
other so far wrong as to have no chance of ultimate success. 



* From avz's, a bird. This comparatively recent French term seems so ap- 
propriate as to warrant its adoption into English. 



Their work will be described separately ; and first that 
of the Aeronauts, in which it will be necessary to describe 
chiefly French achievements, that nation having taken the 
lead hitherto in studies aerial, probably in consequence of 
the invention of the balloon by Mongolfier in 1793. 

AERONAUTS. 

This great step (as it is believed to be) toward a possible 
solution of the problem at first excited the wildest hopes. 
Many believed the navigation of the air to be an accom- 
plished fact. These hopes faded : it was soon found that an 
ordinary spherical balloon was at the sport of the wind ; 
and all sorts of impracticable devices were tried to control 
its motions, save till quite recent years (1852) that of fur- 
nishing it with a screw and an energetic motor. 

While it is possible to impart low velocities, in calm air, 
to any kind of a balloon, yet the motive power which it 
could lift has been so small, and the consequent speed so 
inferior to that of ordinary winds, that until 1884 no bal- 
loon had ever come back to its starting-point. 

We can perhaps best realize this deficiency of motive 
power by calculating approximately the speed which can 
be imparted to a spherical balloon by the motor it is ca- 
pable of lifting ; and instead of selecting one of those gen- 
erally employed in ascensions, of 30 or 40 ft. diameter, we. 
will take as an illustration the great captive balloon built 
and operated by Giffard during the French Exposition of 
1878, which was one of the largest and best ever built. 

This was 118 ft. in diameter." Its volume was 882,925 
cubic feet and its gross ascending power was 55,120 lbs. 
As the weight of the balloon proper, its car, appurte- 
nances and fixtures was 30,536 lbs., there remained a net 
ascending power of 24,584 lbs., which might be utilized for 
a motor, its supplies, and a cargo. 

Let us first calculate the resistance of the air to its motion. 

Being a sphere 118 ft. in diameter, the area of its mid- 
section was 10,936 sq. ft. This would not, however, offer 
the same resistance as a flat surface, the experiments of 
Hutton and of Eorda having shown that the resistance of 
a sphere is 41 per cent, of that of a flat surface of area 
equal to its mid-section. 

But to this is to be added the surface of the car and rig- 
ging, as well as that of the motor, its framing and ma- 
chinery conveying power to the propeller. This is gener- 
ally found to be equal to about T V the area of the balloon, 
and as the surfaces are mostly flat, the resistance is usually 



estimated at 50 per cent, that of a flat plane. Reducing 
these two factors to their equivalent flat feet, we have : 

For the balloon : IO ' 936 * 4i = 4j4 g 4 sq> ft< 
100 

t- .i * 10,936 x Ko mM s ., .. 

For the car. etc.: — ^ ±~ = 546 " " 

10 x 100 

Total equivalent flat surface 5.°3° sq. ft. 

We know by Smeaton's tables of air pressures that at a 
speed of 1 mile per hour the pressure upon a flat surface 
is o 005 lb. per square foot, so that at this speed we may 
estimate the resistance of the balloon to be 5,030 x 0.005 
= 25.15 lbs. — that is to say, that a force of but 25.15 lbs. 
continuously exerted would be sufficient to impart a speed 
of 1 mile per hour to this great mass in still air ; and as 
this velocity is 88 ft. per minute, we have for the power re- 
quired : 

25.15 X 88 = 2213.2 feet-lbs., or 0.067 H. P. 

This seems small indeed, but as the power required in- 
creases as the cube of the speed, let us see how fast the 
balloon can be driven by any available motor. 

The net ascending power is 24,584 lbs., but not more 
than half of this (as shown by the subsequent practice of 
Renard and Krebs) is available for the motor. The re- 
mainder is required for the framing, the propeller, the 
transmitting machinery, the stores of fuel or supplies and 
the aeronauts. We will assume therefore 12,584 lbs. for 
the weight of the motor proper, and that this weighs but 
no lbs. per H. P., as was the case with the steam-engine 
used by Giffard in his navigable balloon of 1852. The 
possible H. P. is therefore : 

12,584 

— — = 1 14.4 H. P. 
no ^ ^ 

If we suppose this to be exerted through an aerial screw, 
inasmuch as the best that has yet been publicly tried gives 
out but 70 per cent, of the power applied (the remainder 
being lost in slip), we shall have for the real available 

power T 4-4 x 7 ° _ g Q p^ p g ut as ^ resistance in 

100 
still air requires an effective H, P. of 0.067 H. P. at 1 
mile per hour, and the power required increases as the 
cube of the speed, we have 



8 /"~8o~ 

0.067 4/ 3 = 80 ; ^ — A/ _ . = 10.6 miles per hour, 

r 0.067 

as the utmost probable speed which could have been ob- 
tained with the most energetic motor which this great 
balloon could have taken up into the air. 

How far this would fall short of stemming the prevail- 
ing winds will appear from the inspection of the following 
table, quoted by M. Gatendorf as the average velocities 
of wind observed during a period of ten years in Germany, 
there being during that time per annum : 

82 days of wind not exceeding 11. 18 miles per hour. 
244^ " " " " " 22.37 " " 

38 " " " " " 42.50 " " " 

% day " " " " 89.48 " " " 

So that the occasions would indeed have been few upon 
which this air ship could have made any headway ; yet had 
its possible speed been 25 miles per hour, it might have 
gone out about three-quarters of the days in the year ; but 
in order to attain this speed it would have required a motor 
of nearly 1,500 H. P., which evidently it was quite impos- 
sible for it to lift. 

Moreover, the recorded wind velocities are generally 
observed near the surface of the ground ; but at compara- 
tively moderate altitudes, say 1,000 to 1,500 ft. above the 
earth, they are much greater. Records kept at the top of 
the Eiffel Tower for 101 days (June to October, 1889) show 
an average velocity of 15.75 miles per hour, while a similar 
instrument 925 ft. lower down registered during the same 
time an average speed of but 4.90 miles per hour, or less 
than one-third of that at the top, 994 ft. in the air. 

It is probably for lack of a realizing knowledge of this 
peculiarity that so many past experiments with navigable 
balloons have proved such disappointments. The aero- 
nauts measured the speed of the wind at the surface, and 
only went up into the air to be swept away by a swifter 
current. 

In view of the fact that wind velocities are much greater 
at sailing heights than at the surface of the ground, the 
opinion may be expressed that aerial navigation cannot be 
accounted even a partial success until a velocity of 30 
miles per hour is obtained ; but in order to remain well 
within the bounds of possibilities, the comparisons here- 
after to be made will be based upon a speed of 25 miles 
per hour. 

This brings us naturally to inquire as to what has thus 



far been done. It is clear that nothing was to be expected 
from any attempt to drive spherical balloons ; that the re- 
sistance must be diminished in some way ; and yet it took 
79 years for aeronauts to realize the fact ; for although 
General Meusnier had proposed them, and Robert Brothers 
had experimented with elongated balloons as early as 1784, 
it was not until 1852 that Henri Giffard, the future inventor 
of the injector, laid down the foundation for eventual suc- 
cess by ascending with a spindle-shaped air ship driven by 
a steam-engine. 

GIFFARD'S BALLOON OF 1852. 

On September 24, 1852, Giffard, then a young engineer 
27 years of age, ascended from Paris in an elongated bal- 
loon filled with ordinary coal gas, driven by an aerial screw 
propeller actuated by a steam-engine ol his own design- 
ing. He was at that time quite poor ; but having been pos- 
sessed since the age of 18 with the conviction that success 
was possible, he had communicated his enthusiasm to two 
of his college friends, who possessed limited means, and 
the three had contrived, amid many discouraging difficul- 
ties, to build and to equip this first navigable balloon. 

It was in shape a symmetrical spindle, 144 ft. long and 
39 ft. in diameter. The screw was three bladed and n 
ft. in diameter. The steam-engine was 01 3 H. P., and 
weighed with the empty boiler 330 lbs., or no lbs. per 
H. P. In proportion to its power, this engine was much 
lighter than any previously built ; but it was the utmost 
weight of motor which the balloon could lift, after making 
due allowance for the weight of the apparatus, its appur- 
tenances, the aeronaut, the fuel, and the water. For the 
two latter 678 lbs. were allowed, of which 132 lbs. were in 
the boiler. Coke was employed as fuel, and the danger of 
setting on fire or exploding the gas escaping from the 
balloon was guarded against by surrounding the grate 
with a tight ash-pan, which again was surrounded with a 
vertical due sheet. Thus no flame came into contact with 
the outer air, and the products of combustion, cooled in 
the return flue, were projected downward through an in- 
verted smoke pipe, into which the steam from the cylinder 
was exhausted. 

The cubic contents of the air ship were about 88,300 
cub. ft., and being inflated with coal gas, its lifting power 
was 3,978 lbs. Had pure hydrogen been used instead, the 
lifting power would have been about 6, 160 lbs., and a 
heavier motor could have been used ; but this would have 



8 

made little practical difference in the results as to speed. 
Fig. I. is a side view of the entire apparatus. The surplus 
lifting power being only sufficient to carry up one man, 
Giffard went up alone, at about 5.15 in the evening. The 
wind on the day previously selected for the ascension blew 
with considerable force, and Giffard knew from his calcu- 
lated resistances that he could not hope to stem it ; but hav- 
ing attained an altitude of about 5,000 ft., he set the engine 
in motion. With no revolutions of the screw per minute, 
he was enabled to get a proper speed of the apparatus^ 
which he estimated at 4.27 to 6.70 miles per hour, so as to 
deflect and turn the balloon from the line of the wind ; and 
thus, while satisfied that this first air ship was quite unable 
to cope with the wind that day or with those generally 
prevailing, he yet was enabled to announce his deliberate 
conclusion that ultimate success was certain with a larger 
balloon and a more energetic motor. 




He further expressed his belief, as a result of this exper- 
iment, " that the danger resulting from the juxtaposition of 
fire and an inflammable gas might prove to be quite illu- 
sory ;" but yet no other aeronaut since his time has dared 
to repeat the experiment. 

He came down in safety just after dark, though not 
without some danger. It was clear that in order further 
to reduce the resistances a still more elongated balloon 



would be required, and he resumed his studies and designs 
for further experiments with unimpaired enthusiasm ; but 
the means of himself and friends were so far exhausted 
that it was only in 1855 that he was enabled to make a 
second trial with what he considered an improved appa- 
ratus. 

This new balloon was 230 ft. long and 33 ft. in diameter, 
being thus 7 to 1 instead of 3! to 1, as in the former experi- 
ment. This change, which was made to reduce the resist- 
ance, resulted in such longitudinal instability as nearly to 
cost Giffard his life. He was on this occasion enabled to 
take up a companion (ML Gabriel Yon) to assist in the 
manoeuvres, but notwithstanding this, the balloon would 
not keep a level keel. The wind blew, and although he 
attained greater speed than on the former occasion, he was 
unable to stem the current for more than a few minutes 
at a time, with all the power of his engine. One end of 
the balloon tipped up, and the flow of the gas tow r ard that 
end aggravated the evil. The valve was at once opened, 
and the aeronauts came down as rapidly as they could ; but 
just as the ground was struck with considerable violence, 
the gas bag, tipping up more and more, slipped out of the 
netting and went to pieces. 

This accident did not alter Giffard's conviction of ulti- 
mate success, but he determined first to make a fortune. 
He shortly thereafter invented the injector and eventually 
became a millionaire, while at no time did he abandon his 
aeronautical studies. 

In order to work out practically all the detail as to gas- 
tight envelopes, stability, appliances, manufacture of hy- 
drogen, etc., he built in 1867 the great captive balloon for 
the Paris Exposition of that year. In 1868 he built one in 
London, and again in 1878 he carried out further improve- 
ments in a new captive balloon at the Paris Exposition, 
this being the one which has already been alluded to. 

At length, in 188 1, he determined upon the construction 
of a gigantic air ship, to contain 1.766,000 cub. ft. of hy- 
drogen and to cost $200,000, out of which he expected a 
speed of nearly 45 miles per hour ; but he was near the 
end of his career. First his health failed, and then his 
eyesight ; he became a recluse ; and finally, discouraged 
and maddened by physical pain,, he died by inhaling chlo- 
roform in April, 1882. 

Giffard was thus the first to drive a balloon with a motor, 
and this he did with a steam-engine. It is probable that 
men before now have gone into a powder magazine with 
a lighted torch and have come out in safety ; still the prac- 



IO 



tice is not to be commended. So Giffard went up with a 
lighted steam furnace under a gas bag open to the air 
through its lower valve and he came down safely not 
once only, but twice ; and yet other aeronauts believe the 
practice so dangerous that not one thus far has repeated 
the experiment. 

THE DUPUY DE LOME BALLOON, 1872. 

During the siege of Paris, in 1870, some 65 ordinary bal- 
loons left the beleaguered city, but notwithstanding many 
efforts, not one of them succeeded in getting back. The 




Government decided in October upon building a navigable 
balloon, to restore communications, and entrusted its 
construction to M. Dupuy de Lome, Chief Naval Construct- 
or, to whose skill was largely due the success of the earlier 
armored ships of France. He went most carefully into the 
questions of balloon resistances, stability and working de- 
tails, and pushed the construction as fast as the disorgan- 
ized industry of the city would permit ; but nevertheless 
the apparatus was completed only a few days before the 
capitulation. 



Then came the insurrection of the " Commune," so that 
it was only on February 2, 1872, that the merits of the air 
ship could be tested. 

The balloon was also a symmetrical spindle, n8| ft. 
long and 48! it. in diameter (2.43 to 1). It contained 
120,088 cub. ft. of pure hydrogen, and its lifting power was 
8,358 lbs. Its principal features of novelty were a syste*m 
of triangular suspension, by which all weights were con- 
centrated at a single point a short distance above the car, 
and the introduction inside of the gas bag of an air pocket 
or bag, say one-tenth in cubic displacement of that of the 
balloon, so as to keep it distended and rigid at all times, 
by blowing in or letting out air. This valuable device was 
found to remove, for low velocities at least, the danger of 
deformation from end thrusts or resistance of the air. We 
shall find it used again in the Renard and Krebs experi- 
ments of 1884-85. Fig. 2 is a side view of this air ship. 

Dupuy de Lome's ultimate purpose was that his balloon 
should be driven with an engine of some sort ; but from a 
wholesome dread of fire, he tried his experiment with hand 
power. The total crew consisted of 14 men, of whom 8 
laborers turned a winch, imparting 27-J revolutions per 
minute to a two-armed aerial screw 29^ ft. in diameter. 
This drove the apparatus at a speed estimated at 6.26 miles 
per hour, with an expenditure of say 0.8 H. P. It is be- 
lieved that the speed was overestimated, but in any event 
it proved insufficient to stem the wind on the day of the 
trial. Dupuy de Lome estimated that by substituting a 
steam-engine of 8 H. P., representing the weight of 7 men, 
or say 1,200 lbs., he could obtain a speed of 13^ miles per 
hour ; but the experiment was not made, and the next in 
date was 

THE TISSANDIER ELECTRICAL BALLOON, 1883. 

Impressed with the belief that recent improvements in 
electrical engines afforded a safe and convenient motor for 
balloons, M. Gaston Tissandier, the distinguished author 
and aeronaut, constructed in 1883, with the co-operation 
of his brother, a navigable balloon 92 ft. long and 30 ft. 
in diameter (3.04 to 1), inflated with 37,439 cub. ft. of 
hydrogen, and with a lifting power of 2,728 lbs. 

The netting in this case was formed of flat ribbons 
sewed to longitudinal gores, which arrangement was found 
materially to diminish the air resistance due to the ordi- 
nary twine netting. The apparatus was driven by a Sie- 
mens dynamo weighing 99 lbs., actuated by a primary 



12 



battery (bichromate of potash) weighing 517 lbs. more 
and capable of developing i-J H. P. for 2^ hours. The 




Fig- 3- 

screw was 9.18 ft. in diameter, with two arms, and was 
rotated at 180 revolutions per minute. Fig. 3 shows this 
apparatus. 

Two ascensions were made. The first was on October 
8, 1883. On this occasion there was almost no wind at the 
surface, but at a height of 1,600 ft. it was blowing at 
the rate of about 6.7 miles per hour. It was found that 
the apparatus was just able to stem it, exerting the full 
power of the motor. After performing various evolutions 
the aeronauts came down, intending to go up again the 
next day ; but the weather being cool, the bichromate so- 
lution froze during the night, and although the balloon had 
apparently lost no gas, it was decided to empty it and to 
try it again after making some modifications in the rudder, 
which had not been found to work well. 

The second ascension took place September 26. 1884, 
and on this occasion the balloon was found to obey its helm 
perfectly, to perform various evolutions and to attain a 
speed which, although inferior to that of the wind that 
day, was estimated by M. Tissandier at 9 miles per hour. 
This probably was also an overestimate. The longitu- 
dinal stability was satisfactory, and the necessary endwise 
rigidity was secured by maintaining an internal compres- 
sion in the gas bag by means of a safetv valve. 

In neither trial could the air ship return to its starting- 
point because of the wind, and the results were so far in- 
ferior to those obtained at about the same time by the 



i3 

French War Department, that these costly experiments, 
which had been carried out at private expense, chiefly in 
the interest of science, by two gentlemen of limited means, 
were not prosecuted further. They had pointed out the 
way, and established that by the substitution for steam of 
electric power, the following advantages were gained : 
i. All danger from firing the gas was avoided. 

2. The apparatus did not vary in weight. 

3. The motor was more easily managed. 

Others stepped in with abundant backing to carry on the 
evolution of the problem. 

FRENCH WAR BALLOON, 1884-1885. 

The aeronautical establishment of the French War 
Department, at Calais, was reorganized in 1879. There 
had been a similar establishment under the first French 
Republic, which had rendered some service by observing 
the enemy from captive balloons, but it had been disband- 
ed. The new organization, which was chiefly intended to 
manufacture and man captive balloons, was in charge of 
able men, who had sufficient means to experiment, and 
the advantage of knowing all that had been accomplished 
by their predecessors. Giffard had pointed out the path, 
Dupuy de Lome had gone into the mathematics ot the 
question in an elaborate memoir, and Tissandier had ex- 
hibited the advantages of electric motors. The French 
officers in charge, Messrs. Renard and Krebs, improved 
very greatly upon all previous practice, and built, in 1884, 
an elongated balloon 165 ft. long by 27^ ft. in diameter, in 
which the largest section was no longer placed midway of 
the spindle, as in all previous attempts, but toward its 
front end, as obtains in the case of birds and fishes. 
Moreover, they placed the screw in front instead of behind, 
as previously practised ; but the great improvement con- 
sisted in largely increasing the energy of the motor in pro- 
portion to its weight. Besides this, they obtained stabil- 
ity and stiffness by the use of an internal air bag and a 
better mode of suspension, and they enclosed the whole 
apparatus in a shed, so that it might be kept permanently 
inflated and await calm days for experiment. 

This air-ship, which was named La France, held 65,836 
cub. ft. of hydrogen, and its lifting power was 4,402 lbs. 
The car was very long (105 ft.), in order to equalize the 
weight over the balloon and yet admit of both being placed 
close together, in order to bring the propelling arrange- 
ments as near the center line of gravity as possible. The 



screw was placed on the car ; it was with two arms, and 
23 ft. in diameter. The power of the motor was ascer- 
tained by experiment in the shop to amount to 9 H. P., 
and speeds of 17 to 20 miles per hour were expected with 
46 revolutions of the screw. Fig. 4 represents this air- 
ship. 

The first trial was made on August 9, 1884, and on a 
calm afternoon the balloon ascended, proceeded some 2\ 



tFm rn^^ffMfS\ 




Fig. 4. 



miles from the shed, and returned to its original starting- 
point, having proved perfectly manageable, and attained a 
speed of 10J miles per hour. This was the first time that 
a navigable balloon had returned to its landing, and the 
experiment attracted great attention, an account of it be- 
ing, a few days thereafter, presented to the French Acad- 
emy of Sciences. The aeronauts believed they could make 
still greater speed, but for obvious reasons they jealously 
guarded such details of construction as were not apparent 
from casual inspection in the air, and more particularly the 
construction of their motor and battery, concerning which 
more will be said hereafter. 

A second ascension was made on September 12, 1884 
(14 days before the last ascension of Tissandier), but al- 
though a speed of over 12 miles per hour was attained, an 
accident to the machine (heating of journals) compelled 
landing at Velizy, instead of returning to the starting- 
point. The latter was, however, successfully accomplished 
again, November 8 following, when two ascensions were 
made on the same day, and a speed obtained of 13.42 miles 
per hour. 

Various minor improvements were made in the appa- 
ratus, and in the ensuing year three more trial trips were 
taken, making seven in all, on five of which the balloon 
returned to its starting-point, as follows : 



15 



SCHEDULE OF TRIAL TRIPS OF "LA FRANCE.' 



No. 




Rev. 


Speed, 




of 


Date. 


of 


Miles 


Remarks. 


Trial. 




Screw. 


per 

Hour. 




i 


August 9, 1884. 


42 


10.24 


Returned to Chalais. 


2 


Sept 12, 1884. 


50 


12.19 


Accident — descent at Velizy. 


3 


Nov. 8, 1884. 


55 


13.42 


Returned to Chalais. 


4 


Nov. 8, 1884. 


35 


8-54 


11 Ik tk 


5 


August 25, 1885. 


55 


13.42 


High wind ; descent at Villacoubray. 


6 


Sept. 22, 1885. 


55 


13.42 


Returned to Chalais. 


7 


Sept. 23, 1885. 


57 


14.00 


(« U tl 



From these experiments, which, it must be remembered, 
were tried merely to test the efficiency out of doors of a 
new war engine, Captain Renard, while stating that the 
resistance was greater and the speed less than he had at 
first expected, deduced the following formulas : 



(1) 

(2) 
(3) 



R = 0.01685 & V* 
JV= 0.01685 D 2 V s 
T = 0.0326 D 2 V\ 



in which 

R is the air resistance to motion in kilogrammes. 

V " " speed in meters per second. 

D " " diameter of the balloon. 

IV i( " work done in kilogrammeters. 

T ** " " " on the shaft of the screw. 
From this he calculates that a balloon 32.8 ft. in diame- 
ter would require 43J H. P. to drive it at 22 miles per 
hour. 

Since 1885 no outdoor experiments have been made so 
far as the public is aware, but it is understood that nu- 
merous experiments have been actively carried on within 
doors, which, being intended to improve a war engine, have 
been surrounded with profound mystery. 

A year or so ago this policy of secrecy was apparently 
changed, and Commandant Renard began publishing a 
number of scientific papers upon various branches of the 
subject, such as the resistance of air, his experiments with 
aerial screws, the possibility of success with aeroplanes 
and the construction of his primary battery, which, after 
having been kept secret for a time, he now fully describes 



i6 

and figures, with the remark that " this publication now 
threatens no danger to the national security," from which 
it is not unreasonable to infer that he has found a more 
efficient motor, and that it is not electric ; for he says 
further : " In the actual condition of industrial electricity, 
it is impossible that an electrical balloon shall constitute a 
true war engine." 

At the Paris Exposition of 1889, the War Department 
erected a special building, and exhibited the air-ship La 
France, together with all its belongings, including the 
motor, battery, screw, etc., and full accounts of these ex- 
hibits have been published in various technical jour- 
nals. 

And yet the impression was produced on many minds 
while in Paris, more perhaps from what was not said 
than from what was shown and published, that the French 
War Department was, even now, in possession of impor- 
tant improvements and information which will afford in- 
creased speed, but which, as is right and proper, are kept 
secret, to prevent their use by possible enemies. 

Should this conjecture be correct, it is not impossible 
that, in case France should be involved in a European 
war, we should soon see navigable war balloons flying at 
the rate of 25 to 30 miles per hour, going out over the 
enemy's lines on reasonably calm days to observe his po- 
sitions and to drop an occasional explosive on his head. 
Indeed, in some of his writings, Commandant Renard, 
after laying down that " the conquest of the air will be 
practically accomplished when a speed of 28 miles per 
hour is obtained," expresses the opinion that we are on 
the eve of freely navigating the air, and that probably 
France will possess the first aerial Meet. 

It is stated that the German, Russian and Portuguese 
Governments have recently organized aeronautical estab- 
lishments, and are experimenting in secret. Should some 
notable success follow, it will not be the first time that a 
great invention has been advanced by the necessities of 
war. 

Leaving speculation, however, the accompanying table 
gives the principal data as to the four air-ships which have 
been described, and the H. P. necessary to drive them at 
25 miles per hour. 

The last line shows how light a motor must be to pro- 
duce 25 miles per hour without increasing the weight. 

We will consider the all-important question of motive 
power after examining the probable requirements of ap- 
paratus heavier than the air. 



\1 



SCHEDULE OF NAVIGABLE BALLOONS. 



Data. 



Length, out to out ft. 

Diameter, largest section " 

Length to diameter. . .proportion 

Cubic contents ft. 

Ascending power lbs. 



Giffard, 
1852. 



Wei 



ght — Balloon and valves, " 
Netting and bands, " 
Spars and adjuncts, "• 
Rudder and screw, " 
Anchor and guide 

rope " 

Car complete " 

Motor in working 

order " 

Aeronauts ' l 

Ballast and supplies " 

Total apparatus u 



H. P. of motor 

Weight of motor per H. P., lbs. 
Speed obtained. . .miles per hour 
H. P. required 25 miles per 

hour 

Motor lbs. per H. P 



144-3 

39-3 

3.67 to 1 

88,300 

3»978 



704 
33o 
660 



176 

924 



462 

i54 
567.6 



3,977-6 



3 

J54 

6.71 

3 



Dupuy 

de Lome, 

1872. 



118.47 

48.67 

2-43 

120,088 

8,358 



1,255 5 

396 
1,316.5 

165 

308 
1,287 

2,000 

310 

1,320 



8,358 



Tissan- 
dier, 



0.8 
2,500 
6.26 



5*(?) 

38(?) 



91.84 
30.17 
3-o4 
37,439 
2,728 



374 
154 
75 



no 
220 



616 

330 



2,728 



IS 

410 
6. 7 i 

77 



Renard & 
Krebs, 
1884-85. 



165.21 

27-55 

6 

65,836 

4,402 



812 
279 
170 
193 



995 

1,174 
308 
47i 



4,402 



9 
130 

'4 

5i 
23 



POSSIBLE IMPROVEMENTS IN BALLOONS. 

Before expressing an opinion upon the future speed of 
navigable balloons it may be interesting to review the 
various difficulties which have hitherto been met, and to 
inquire into what patent attorneys call " the state of the 
art." 

The greatest speed thus far attained has been 14 miles 
per hour, which, as indicated at the beginning, is insuffi- 
cient to cope with most of prevailing winds, particularly 
at sailing heights above the ground, and the following 
difficulties have been encountered and, to a certain ex- 
tent, overcome. 

1. Excessive loss of gas in early experiments. 



This has been remedied by closer tissue of envelope and 
better varnishes, as well as by regulating valves, so that 
the loss of gas at the captive balloon in Paris last summer 
was said to average less than 2 per cent, per day. 

2. Resistance of air to forward motion. 

This has been largely diminished by pointed ends, but 
much remains to be done in ascertaining the best propor- 
tions. 

3. Need of a propeller to act on the air. 

This has been measurably solved by the aerial screw, 
which is said to exert from 50 to 70 per cent, of the power 
applied, but is yet less efficient than the marine screw, 
which works up to 84 per cent. 

4. Need of steering gear. 

This has been fairly worked out by various arrangements 
of rudders and keel cloths, which have given command of 
the apparatus when in motion. 

5. Need of a light motor. 

This is the great difficulty. Steam has been tried with 
a weight of 154 lbs. per H. P., including fuel and water, 
and electric engines with a weight of 130 lbs. per H. P. 
Neither are sufficiently light to give the necessary speed, 
except, as will be explained, for very large apparatus. 

6. Need of endwise stiffness. 

This has been remedied by compressing the gas inside 
the balloon, either through the use of a loaded safety valve 
or through the use of an internal air bag. As speed in- 
creases more will needs be done in this direction, and this 
will require stronger and heavier envelopes for the gas bag. 

7. Need to prevent deviations in course. 

This has been overcome by placing the screw in front, 
where it is more effective than behind. 

8. Need of longitudinal stability. 

This has only been partly solved by various methods of 
suspension. There is still a tendency to pitch when meet- 
ing gusts of air, and this will increase when greater speeds 
are attained. It will need to be worked out by experiment. 

9. Need of altitudinal stability. 

This is the tendency of the balloon to rise or fall with 
the heating or cooling of the gas. It has been met in 
only a crude way by alternately discharging either gas, 
to prevent the balloon from bursting, or ballast,*to prevent 
it from coming down. This rapidly exhausts both gas 
and ballast, and limits the time of the trip. 

It has been repeatedly proposed to substitute for this 
method a vertical screw, to raise and depress the balloon, 
which should then be at starting slightly heavier than the 



J 9 

air which it displaces ; and one of the best proposals for 
this purpose is due to an American engineer, Mr. E. Fal- 
connet, who patented it in 1885, together with many other 
features, to remedy the various difficulties which have been 
encountered ; but death cut short his labors, and his de- 
vices have never been experimented on. 

The great desideratum is to gain increased speed, and 
there are at least four ways by which this may be accom- 
plished. 

1. By giving the balloon a better form of hull, so as to 
diminish the resistance. La France was rather blunt in 
front, and there is reason to believe that by simply moving 
the largest section further back, increased speed will result. 

2. By designing a more efficient aerial screw. Com- 
mandant Renard has been experimenting in this direction, 
and says there is a shape much better than others, and 
that this form cannot be departed from without getting 
very bad screws ; falling, as he expresses it, into a veri- 
table precipice on either side. 

3. By devising a lighter motor, in proportion to its 
energy. This is the great field in which work remains to 
be done. It was announced in September, 1888, by a 
newspaper correspondent that Commandant Renard had 
built a motor weighing 1,100 lbs. and developing 50 H. P., 
but since then nothing has been heard of it. 

4. By simply building larger air-ships, for, inasmuch as 
their contents, and consequent lifting power, will increase 
as the cube of their dimensions, while their weight will, 
approximately, only increase as the square, the surplus 
lifting power will evidently increase with the size, and 
greater motive power in proportion can be used. 

Let us suppose, for the sake of this argument, that no im- 
provement whatever has been achieved in either of the first 
three ways which have been mentioned, and inquire simply 
what would be the effect of doubling the dimensions of La 
France. The comparison will be approximately as follows : 



Principal Dimensions. 



Double Size. 




Length, out to out ft. 

Diameter, largest section " 

Contents of gas cub. ft. 

Lifting power lbs. 

Weight of apparatus " 

" Cargo and aeronauts <; 

" Machinery " 



20 

As the motor (dynamo and battery) of La France 
weighed 130 lbs. per H. P., we have for that of double the 

23,912 
S1Ze ~1no ~ l82 H# P * motor > and calculating the speed 

by the formula of Commandant Renard, and inserting the 
new diameter, 16.8 meters, we have : 



T — 0.0326 X 16.8' 2 x V 3 in kilogrammeters. 

But as we have 182 H. P., and there are 7$ kilogram- 
meters in the H. P., we have further : 

182 x 75 = 0.0326 x 16J 2 X V\ 

whence V = i/ = 11.2 meters. 

' 9.2 

So that we see that the speed of the new air-ship will be 
11.20 meters, or 36.7 ft. per second, say 25 miles per hour. 

The same result is arrived at by considering that the 
new balloon will require four times the motive power of 
La France to go at the same speed, and that the power re- 
quired increases as the cube of the speed. So that we see 
that a speed of 25 miles per hour is even now in sight, 
without any other improvement than doubling the size of 
the balloon. 

It will not be safe to assume, however, that increased 
speed can be indefinitely obtained with mere increase of 
size, because with more speed a series of new difficulties 
are likely to arise, and some of the old ones to be aggra- 
vated. 

The first of these will probably come from the lack of 
longitudinal stiffness. Although it has been found that a 
certain amount of internal gas pressure gives the elongated 
balloon sufficient rigidity to resist the pressures due to low 
speeds, so soon as these are increased there may be a 
tendency to buckle, twist and collapse, and this means 
more pressure, a stronger envelope and more weight ; or 
a rigid internal frame, as proposed by Mr. Falconnet ; and 
this also means much more weight. 

Next, there will be in great balloons much greater diffi- 
culty in distributing equally the weight of the car and its 
contained motor over the gas-bag, because of the neces- 
sary greater concentration of weight in the car. It will 
besides be found more difficult to apply the propelling 
power near the line of equilibrium, so as to avoid oscilla- 
tions. 

There will also be increased difficulty from the flow of 



2\ 



the gas back and forth inside of the elongated balloon, 
thus displacing its center of gravity, and threatening the 
danger which so nearly proved fatal to Giffard. Moreover, 
even slight changes of outer temperature, heating and 
cooling the gas in the balloon, and thus changing its as- 
cending power, are likely to be far more troublesome when 
operating on large than on small masses of gas, so that it 
seems likely that large balloons will be found more un- 
stable, both vertically and longitudinally, than the compara- 
tively moderate sizes which have so far been experimented 
upon. 

These difficulties can all be surmounted, no doubt, in- 
cluding the remaining one that large balloons will be cost- 
ly, and that few can afford to experiment with them ; but 
the various appliances necessary for stability will involve 
more weight, and this again will require more size. 

Be this as it may, it is evident that somewhere a limit 
will be reached beyond which unmanageable sizes will be 
met with. The weight, the size, the resistance will in- 
crease, as well as the speed, and somewhere there will be 
impracticability. We have seen that to go 25 miles per 
hour, and thus brave the wind about three-quarters of the 
time, we need an elongated balloon similar in shape to La 
France, 330 ft. long and 55 ft. in diameter. It is probable 
that, by improvement in the first three ways which have 
been mentioned, it may attain a speed of 30 or 35 miles 
per hour ; but when it is attempted to obtain 40 miles per 
hour out of it, it will grow to lengths of, say, 1,000 ft., or 
as long as four ordinary city blocks, and diameters of 150 
ft., or the height of an ordinary church steeple. 

These seem unmanageable and impracticable sizes for or- 
dinary uses. They are greater than those of ocean steam- 
ers, because the speed required is greater, to overcome the 
aerial currents ; and the care and maintenance of these 
great air-ships will be a difficult matter. 

It seems likely, therefore, that in the near future elon- 
gated balloons will be built which will be driven at 25 or 
30 or a few more miles per hour, which will be able to 
sail about on all but stormy days ; but the cargoes carried 
in proportion to the size will be small, and to obtain 
speeds similar to those of express trains some other form 
of apparatus will have to be sought for. 

PART II.— AVIATION. 

Having sketched what has thus far been accomplished 
with, and what may be fairly expected from navigable 



22 



balloons, we may next turn our attention to that other 
class of students who call themselves t% Aviators," and 
who, discarding the use of a gas-bag, seek to solve the 
problem ot flight by purely mechanical means. They 
point to the birds in confirmation of their views, and con- 
stitute by far the most numerous as well as the most an- 
cient school ; for, to say nothing of ancient traditions, 
earnest proposals have been brought forward during the 
last 400 years to compass flight by various mechanical 
contrivances. 

With these students, the possibility of success has been 
more a matter of faith, of instinctive belief, than of sober 
calculation. They watched the birds, saw that they pro- 
gressed through the air by mechanical action and skill, 
and were very much heavier, bulk for bulk, than the air 
which their bodies displaced (for we may dismiss with a 
smile the old-time assertion that birds gain levity by in- 
flating their quills with heated air), and they hoped that 
man might accomplish similar results by somewhat similar 
means. 

Impressed with these views, a number of these students 
have organized aeronautical societies in Great Britain, in 
France, and in Germany, and have for the past 20 odd years 
been reading papers, discussing the subject, and trying 
sundry experiments. 

Very little practically has thus far come from these 
efforts, for curiously enough, and yet naturally, the first 
endeavors were to devise or to construct models, which 
have remained toys, before knowing accurately the resist- 
ances and conditions which they were to encounter in the 
air. In other words, the work began upon the construc- 
tive instead of the analytical features of the case, as usu- 
ally happens at the outset of an invention, and while a 
good deal of valuable information has. been gathered, no 
practical machine has yet resulted. Some theoretical in- 
vestigations have been attempted, but unfortunately the 
scientists have been hopelessly at variance not only among 
themselves, but also, what is more important, with some 
of the ascertained facts. 

Thus it has been so far unknown what power birds ex- 
pend in overcoming the resistance of the air in their flight, 
or what amount of support they derive from it at various 
angles ; and although the laws of fluid resistances laid 
down by Newton are known to be erroneous, they are 
still taught in the academies ; and it was only the past 
summer that a new theory of flight, which may prove to 
be the correct one, was proposed simultaneously by two 



civil engineers at the Aeronautical Congress of the Paris 
Exposition. 

Even the theory of the equilibrium of the common kite, 
supposed to have been invented by Archytas 400 years 
B.C., is still a subject of dispute, and every little while a 
fresh solution of its numerical reactions is proposed by a 
mathematician. 

Possibly, in consequence of this state of uncertainty as 
to the laws of flight, the Aviators have been divided into 
three camps or sub-schools, which have looked for success 
from somewhat different contrivances, and who have ad- 
vocated the following mechanical means : 

1. The imitation of the flapping action of the wings of birds. 

2. The sustaining of weight and obtaining progress 
simultaneously through the air by horizontal screws. 

3. The sustaining of weight by fixed aeroplanes, and 
the obtaining progress by means of screws. 

A great many experiments have been tried and a great 
deal of ingenuity has been expended in each of these three 
directions, but thus far not a machine has been able to 
leave the ground with its prime motor, and what meas- 
ure of success has been attained can only be exhibited 
through toys, which give an idea of the principles in- 
volved. 

The advocates of wing action hold that nature cannot 
err in her methods, and that success is only to be achieved 
by imitating her ; they have therefore endeavored to de- 
vise moving surfaces which shall repeat the complicated 
movements of the wings of birds, so as simultaneously to 
sustain and propel the apparatus. The only motive power 
which it has thus far been found practicable to use has 
been the torsion of india-rubber, and with this a number 
of clever mechanical birds have been contrived by Mr. 
Brearey in England, and by MM. Penaud, Tatin, de Ville- 
neuve and Pichancourt in France. 

The latter — that of Pichancourt — dates only from last 
summer, and is represented by fig. 5. 

It measures about 12 in. from tip to tip of wings, and 
weighs 385 grains, one-third of which consists in the 
twisted rubber strings furnishing the motive power. The 
necessary flexion of the wings, to obtain a propelling as 
well as a sustaining reaction, is produced by a triple ex- 
centric, each actuating a lever fastened to a different point 
in the wings. 

Upon being wound up and released, the apparatus flies 
slightly upward, and to a distance of 30 to 60 ft., in from 
3 to 6 seconds. Similar but larger birds, of the same 



24 




Fig. 5- 

make, are said to have flown up to a height of 25 ft. and 
a distance of 70 ft. against a slightly adverse wind. 

The relative power absorbed, however, is quite beyond 
the capacity of any known prime motor. 

The next principle — that of an aerial screw to sustain 
and to propel simultaneously by its horizontal revolution — 
was actively promoted in France some 25 years ago, and 
great results were expected. It was proved, however, that 
it required about 1 H.P. to sustain S3 ^ DS - m tne a * r > or 
much more than the energy of any engine, and the sole 
survivors of the many experiments made are the various 
flying screws which still amuse children ; the best of these 
being that of Penaud, shown in fig. 6, in which two screws 
rotate in opposite directions and cause the apparatus to 
rise or to fly in a circle, according to the proportions of 
its various parts. 

And lastly, in recent years, experiments have been made 
with combinations of fixed surfaces, called aeroplanes, to 
sustain the weight, and of rotating vertical screws to pro- 
pel. Machines or models on this principle have been 
built by Henson, Stringfellow and Moy in Great Britain, 



25 



and by Penaud, Tatin, de Louvrie, and du Temple in 
France, but thus iar not one has succeeded in lilting a 




Fig. 6. 



self-contained motor, and perhaps, after all, the best ex- 
ample of this class of contrivance is the artificial butterfly 
of M. Dandrieux, which is shown in fig. 7. 




Fig. 7- 



The flight of all these toys lasts but-a few seconds, and 
none of them carries its own motive power, while it will 
be found by measuring accurately the foot-pounds ex- 



26 

pended, and the weights sustained in a given time, that 
not one of the prime movers known is as yet sufficiently 
light, in proportion to its energy, to furnish the power 
required to maintain them in the air. 

This question of motive power, the vital one in Aerial 
Navigation, will be discussed more particularly hereafter, 
but it may here be mentioned that a few observers, who 
have been watching birds soar without flapping their 
wings in southern latitudes, believe that this species of 
flight involves no expenditure of pow T er whatever, save for 
the getting under way. This opinion has been much ridi- 
culed, but yet it is possible that if we take into account 
the force of the wind, the belief of these observers that 
certain birds can soar indefinitely at moderate speeds 
without other exertion than the passive one of keeping the 
wings rigidly extended may not be as absurd as at first 
sight appears ; but if man is ever to direct himself at will 
through the air, at satisfactory velocities, he will need 
power, and plenty of it ; more indeed in proportion to the 
weight of the motor and of its supplies than he has yet 
been able to devise. 

Meanwhile a few observers and scientists have been 
patiently investigating the motions which birds perform 
in their flight. Among these may be mentioned the Duke 
of Argyle and his book, " The Reign of Law ;" M. Mouil- 
lard and his " Empire de 1' Air ;" Dr. Petigrew and his 
book on " Animal Locomotion," and especially Professor 
Marey, who has just published a book, " Le Vol des Oi- 
seaux," the result of 20 years' investigation, which is most 
interesting and valuable, but which, unfortunately, throws 
but little light upon the all-important questions as to the 
sustaining reactions to be derived from the air, and the 
power required for flight ; the latter having remained in 
controversy since the days when Navier made the erro- 
neous calculation that a flying swallow exerted one-seven- 
teenth of a H.P., or at the rate of no less than 3,586 H.P. 
per ton of weight. 

Of course, the first thing to ascertain is to know what 
are the components of air pressure upon a plane in motion 
at a given velocity, if inclined to the current. In other 
words, what proportion of the usual right angle pressure 
remains if the plane be tilted, and how much of this new 
pressure acts as a sustaining force or lift, while how much 
opposes forward progress, and may be denominated drift. 
Some interesting experiments have been made in Great 
Britain on this subject, and more of them in France, but 
they have chiefly been made with some form of rotating 



27 

apparatus, and it was found not only that the results ob- 
tained with direct currents did not agree with those of 
rotary machines, but that the latter showed greater pres- 
sures on planes inclined at angles of 50 to jo° than on 
those placed at right angles to the current (a most im- 
probable condition), so that it is now believed that the 
centrifugal force of the rotating vanes in some way vitiates 
the results, and the French have been preparing to try a 
new set of experimenrs upon artificial currents to be pro- 
duced by large ventilating fans. 

Things were in this condition when an International 
Congress of Aeronauts and Aviators was held in Paris 
last August. During this a number of papers were pre- 
sented, and among them were two which may lead here- 
after to a new and more rational theory of flight. One 
was by a Russian engineer, M. Drzewieki, who, starting 
from the best empirical formulae he could find, had cal- 
culated the weights sustained, the surfaces required, and 
the power needed for aeroplanes in ariihcial flight at vari- 
ous velocities, while the second paper was a theoretical 
investigation of the same subject by the present lecturer. 

The remarkable result about these papers was "that. 
starting from two different standpoints— the empirical and 
the theoretical — they closely agreed in their conclusions ; 
and as the paper of M. Drzewieki w r as the most complete 
and thoroughly worked out, I shall prefer to give an ac- 
count of it rather than of my own. 

M. Drzewieki first showed that the hitherto received idea 
that a bird in flapping his wings generated thereby a suffi- 
cient pressure to sustain his weight is incorrect. It has 
long been known that the pressures experimentally ob- 
tained by striking the air with surfaces of equal area and 
velocity with those of the wings of a bird, or even with the 
wings of a dead bird dried and mounted in an apparatus, 
do not generate a sustaining reaction equal to the weight 
of the bird ; but it was dimly believed that the living bird 
had the skill, in some mysterious way, of obtaining from 
his strokes sufficient intensity of pressure to sustain his 
weight. M. Drzewieki says that this view is quite erro- 
neous, and that the bird is really sustained by the vertical 
component of the pressure due to his speed. In other 
words, that the flying animal is really an aeroplane, whose 
body and wings in all stages of their action make a very 
small angle with the impinging air, and that the propelling 
power is chiefly derived from the rear thrust exerted by 
the escaping air against the outer curved extremity of the 
quill feathers. 



28 



Moreover, if account be taken of the forward motion, 
the angle which the wings present to the line of flight 
must be less than 6°. It is imposssible to detect this angle 
of incidence by the eye. The wing seems to be flapped 
vertically downward ; or in soaring the bird seems to hold 
his wings and body absolutely horizontal ; but in point of 
fact we know that there must be an angle of incidence 
in order to obtain a sustaining reaction. This brings up 
the inquiry as to what that angle really is. 

M. Drzewieki starts from Duchemin's empirical formula 
of the normal resistance which air opposes to an inclined 
plane moving against it, and deduces therefrom the sus- 
taining reactions per square meter at various velocities 
for various angles from 20' to io°, and these are tabulated 
for ready reference. Next he calculates the horizontal 
components of the normal pressure for the same velocities 
and angles, this being the resistance to the advancement 
of the plane alone, and to this is added the head resist- 
ance due to the thickness necessary to secure the required 
strength of the plane, or, in other words, its hull resist- 
ance, and to this again is added the probable friction of 
the air against the sides. These three items together give 
the total resistance to forward motion, and are also tabu- 
lated for ready reference. 

Then, by combining these two tables and plotting the 
resulting curves, in order to ascertain at what angle there 
is a minimum of resistance to forward motion, while yet 
retaining a sufficiency of sustaining power, it is found that 
this occurs for one and the same angle at all velocities, 
this being i° 50' 45," and this M. Drzewieki assumes as 
the angle of flight. 

I may here mention that these two reactions, or com- 
ponents of the normal pressure due to the angle of inci- 
dence and to the speed, formed the subject of the paper 
read by myself at the Paris Congress, and of a similar 
paper which I presented before the American Association 
for the Advancement of Science at its last meeting, and 
that I had reached the conclusion that the most favorable 
angle for soaring was between i° and 2 . 

Assuming i° 50' 45" as the angle of flight, and allowing 
for the vertical and horizontal components of the normal 
pressure due to the speed at that angle, as well as for the 
hull resistance and friction, M. Drzewieki then gives four 
formulae, supplemented by tables, which produce the fol- 
lowing elements : 

1. The weights per square meter, which can be sustained 
at this angle of i° 50' 45" at various speeds. 



2. The work done (kilogrammeters) to overcome the 
forward resistances under the same circumstances as 
above, 

3. The proportion of the work done to the weight sus- 
tained. 

4. The amount of surface required to sustain 1 kilo- 
gramme at various velocities. 

The consequences which M. Drzewieki deduces from 
these formulas and the plotting of their curves are the 
following : 

1. An aeroplane progressing horizontally, with the angle 
of incidence (i° 50' 45") corresponding with the minimum 
of work, meets practically the same resistance at all 
speeds, so that the work done is approximately a function 
of the weight of the apparatus, multiplied by the velocity. 

2. Aeroplanes designed for small speeds need relatively 
large surfaces and small weight ; these conditions he be- 
lieves to be difficult of realization in practice. 

3. The greater the speed, the less surface needed to 
support a given weight. 

4. The less the surface, and therefore the greater need 
of speed, the greater must be the motive power. 

These conclusions are believed to be approximately 
sound, and M. Drzewieki sustains them by showing that 
in flying birds the smaller is the sustaining surface in pro- 
portion to their weight, the greater is their customary 
speed, giving a table of the proportions of some 64 birds, 
which shows that the surfaces of the body and extended 
wings range from 7.56 sq. ft. to the pound for the bat, 
which flies at the rate of about 20 miles per hour, to 0.43 
sq. ft. per pound for the male duck, who progresses at 
about 60 miles per hour. He estimates that for a speed of 
90 miles per hour, the surface required will be but 0.22 
sq. ft. to sustain a pound of weight. 

It seems to follow as a conclusion that if aeroplanes are 
ever built to carry tons of weight, their proportion of sur- 
face to weight may be considerably less than those which 
obtain with birds, but that the speed will need to be 
greater than that of flying animals in order to obtain sup- 
port from the air, while the motive power required will 
vary approximately only in the direct proportion of the 
weight carried. This important conclusion seems to hold 
out hopes that success may eventually be attained if the 
stability of the apparatus can be secured. 

M. Drzewieki also discusses this question of stability. 
He shows that the transverse equilibrium can easily be 
maintained by a diedral upward slant of the wings of an 



3o 

aeroplane, arranging them like the sides of the letter V, 
but at a very obtuse angle, so that any tendency to tilt 
shall at once develop greater pressure in that direction, 
and thus restore equilibrium. This was pointed out as 
early as 1809 by Sir George Cayley, in a remarkable series 
of papers published in Nicholson' s Journal, which are 
well worth reading. 

M. Drzewieki states the law of longitudinal equilibrium 
to consist in placing the center of gravity of the whole ap- 
paratus vertically below the center of pressure due to the 
angle of flight, and he gives the rule, first formulated by 
Joessel, for determining this center of pressure. He more- 
over states that these two centers, of gravity and of pres- 
sure, must be but a very short distance apart, in order to 
prevent oscillations. This solution is substantially, for 
flat angles of incidence, the same as that of Sir George 
Cayley, who states that the center of gravity must be at 
right angles to and below the center of pressure ; but it is 
to me doubtful whether this is the best solution for assur- 
ing the longitudinal stability of a flying apparatus, and 
this important, almost vital question is likely to prove a 
stumbling-block in the way of future experimenters. 

Assuming it to be solved, M. Drzewieki estimates that an 
apparatus, built to the best possible proportions as to ex- 
posed surface and form, and sailing at an angle of i° 
50' 45", will require to drive it at 25 miles per hour but 
5.87 H.P. per ton of its weight. This assumes the thick- 
ness of apparatus and consequent hull resistance to be 
but T |o of its horizontal dimensions, while for birds it 
generally runs from 5 to 10 per cent. That is to say, that 
birds exposing a horizontal surface of say 100 sq. in. gen- 
erally expose a maximum cross-section vertically of 5 to 
10 sq. in., while M. Drzewieki believes this can be reduced 
to the proportion of 1 sq. in. per hundred for an aeroplane. 

My own estimate of the power required by a common 
pigeon gliding at an angle of i° with the horizon was 
9.33 H.P. per ton of his weight, and 10.49 H.P. per ton at 
an angle of 2 for this same velocity of 25 miles per hour. 

These are considerably less than the powers required to 
drive a balloon of moderate size at the same speed, for we 
have already seen that the air-ship La France would re- 
quire 51 H.P. to attain 25 miles per hour ; or, as it weighs 
2.2 tons, the motor would needs develop 23.2 H.P. per ton 
of the weight of the whole apparatus. For the balloon of 
double this size, the power required is at the rate of 10.34 
H.P. per ton of apparatus. This power required would 
moreover increase in the case of the balloon, as the cube 



3* 

of the velocity, while M. Drzewieki shows that in the case 
of an aeroplane the power will increase only in the direct 
ratio of the speed, because as the velocity becomes greater 
the area of sustaining surfaces required becomes less, and 
he estimates that an aeroplane will require 10.43 H.P. per 
ton to go 44.72 miles per hour, and 20,62 H.P. per ton of 
its weight at 89,44 miles per hour. 

This brings up the question of possible motors, and if 
we confine ourselves for the present to 25 miles per hour, 
and assume the power required at 10 H.P. per ton of ap- 
paratus, we see at once that only a fraction of that weight 
can be devoted to the motor. Let us assume, and I think 
this is not far wrong, that only one-quarter of the weight 
can be apportioned to the motor and its supplies ; the re- 
maining three-quarters being required for the weight of 
the framing, the aeroplane surfaces, the various appurte- 
nances, and the aeronauts, we then have but = 

4 X 10 
50 lbs, per H.P. as the weight allowable for the motor and 
its supplies for such period of time as it is to consume in 
its trip. This does not greatly differ from the proportion 
in the pigeon, whose pectoral muscles weigh ^J of his 
total weight, or 46 lbs. per H.P., including, it must be 
remembered, the stored-up energy which enables him to 
accomplish long flights without alighting. 

Now, how does this compare with the weight of the en- 32 
gines manufactured by man ? There are three classes of *J 

1. Steam-engines. 

2. Gas-engines. 

• 3. Electric motors. 

The machines in common use, being designed chiefly 
for strength and durability, are needlessly heavy, and it is 
only by inquiring into what has been done for special pur- 
poses that we ahsll get an idea of their possibilities. 

Thus as to steam-engines : Ordinary stationary machines 
weigh with their boilers from 500 to i,6oo lbs. per H.P. ; 
locomotives, from 200 to 300 lbs. ; marine engines for 
Atlantic steamers, 480 lbs. , and light launch engines— those 
of Herreshoff, for instance— some 60 lbs. per H.P. For 
aeronautical purposes, however, a steam-engine was built 
by Stringfellow, which weighed but 13 lbs. and exerted 
1 H.P., and another was built by Moy and Schill of 3 
H.P. and 80 lbs. w T eight, thus being about 27 lbs. per H.P. 

But these weights, while including the boiler, do not in- 
clude the water and fuel. These supplies may be esti- 
mated at 22 lbs. of water and 4 lbs, of coal per hour, so 
that if a large engine can be built as light per H.P. 13 



o 



32 

lbs. as that of Stringfellow, it would still need, if for so, 
short a trip as two hours, 52 lbs. of supplies per H.P. 
making a total of 65 lbs., including the engine itself. 

The principal weight is that of the water. It has been 
proposed to utilize part of this over and over again, by 
equipping navigable balloons with surface air condensers, 
but the difficulties in the way of this, chiefly from the 
added weight, are almost insuperable. 

Next, therefore, gas and petroleum engines suggest 
themselves. As now made they are excessively heavy, 
weighing from 280 to 1,000 lbs. or even more per H.P., so 
that the advantages of dispensing with the boiler and its 
water supply are completely lost. They are comparatively 
of recent invention, however, and it is believed that corre- 
sponding reductions of their weight can be made,* such 
as have been effected for the steam-engine, and as will be 
seen hereafter for electric motors, and that this is a prom- 
ising field for experiment ; for even if aerial navigation be 
an Utopia never to be realized, improvements which will 
permit a reduction in the weight of gas-engines are likely 
to cheapen their cost materially, and to extend their use, 
as well as the profits of their builders. 

And, lastly, we will consider the electric motors, with 
which whatever of success the navigable balloon has so 
far attained has been accomplished. They -involve, like 
the steam-engine, two separate parts, the motor proper 
and the generator, which latter may be either a primary 
battery or an accumulator. 

The weights of the motors or ordinary dynamos used in 
this country run from 92 to 260 lbs. per H.P. developed, 
while abroad they run from 68 to 350 lbs. per H.P. ; but 
the special dynamo used by Commandant Renard 
weighed but 26.4 lbs. per H.P., and a very small one, built 
of aluminium by M. G. Trouve, weighed at the extraor- 
dinary rate of but yj lbs. per H.P. 

M. Trouve is now building for the Portuguese Govern- 
ment a 10-H.P. dynamo, which will weigh less than 220 
lbs., and which is to be used to drive a navigable balloon. 
The total weight of the motor, batteries for several hours 
of work, screw and accessories, is estimated at 1,496 lbs., 
or at the rate of 149.6 lbs. per H.P. developed. 

Contrary to expectation, accumulators are found, by 
comparison of numerous data from various makers, gath- 



* Since reading this lecture, the Author has seen an account of a three-cylin- 
der petroleum engine built for marine purposes, in France, which develops 5 
H.P., and weighs but 440 lbs., thus being in the ratio of 88 lbs. per H.P. It 
consumes, as near as may be, 1 lb. of petroleum per H.P. per hour. 



33 

ered by M. Tissandier, to be actually heavier than primary d 
batteries. As they are charged to last various periods of 
time, it is necessary, in order to compare them, to reduce ^ 
them to the common standard of one H.P. for one o 
hour, and it is then found that accumulators of the best H 
make weigh from 107 to 162 lbs. per H.P. per hour, a fair ^ 
average being 135 lbs. ; while the primary battery of Com- 5 
mandant Renard is stated by himself to weigh but 66 lbs. £ 
per H.P. per hour, and to last a little over 1 hours, this£ 
being the present possible length of his trips. Thus the^i 
into 26.4 lbs. of dynamo and 103.6 lbs. of primary bat- 
tery, making in the aggregate the 130 lbs. per H.P., as 
has already been mentioned. 

It will be observed that all these weights of motors are 
in excess of the 50 lbs. per H.P., which have already been 
assumed as the weight which can be afforded for aerial 
navigation, and yet not so greatly beyond it as to shut off 
all hope of improvement. Hitherto it has not been gen- 
erally realized that the chief obstacle in the way of success 
is the want of a light motive power, one which shall de- 
velop great energy with little weight, and it is possible 
that when inventors turn their attention in this direction 
still lighter motors than at present known shall be the 
result. 

It has been suggested repeatedly that a suitable motor 
for aerial navigation may be found by the invention of 
some kind of explosive engine, utilizing the force of gun- 
powder, nitro-glycerine or some other substance which 
can be flashed irom the solid or liquid form to the gaseous 
condition ; but such a motor is yet to be invented, and, 
what is more difficult, regulated and perfected. Attempts 
in this direction, notably with gunpowder, actually ante- 
date the steam engine, but the difficulties ot controlling 
power so intense and so rapidly generated have hitherto 
- been found too great to be overc >me. It would be rash 
to say that they cannot be, although true explosive engines 
have thus far exhibited an unpleasant irregularity of work- 
ing, frequently giving deficient strokes, but at times com- 
ing out with powerful explosions which may kill the 
inventor. 

It is believed that gas or petroleum engines, which are 
also explosive engines, with the difference that the work- 
ing substance is already in the gaseous form, and thus 
subject to fewer irregularities of expansion, present greater 
chances of success in obtaining a light motor for aerial 
purposes, and would-be inventors are advised to turn 
their attention in this rather than in other directions. 



34 

But even if the motor is worked out, there will remain 
some serious difficulties to be encountered before man can 
fly through the air at satisfactory speeds. The first of 
these is the requirement for absolute stability which has 
already been alluded to. The apparatus must balance 
itself in the air automatically, and must possess sufficient 
surface to come down as a parachute should the machinery 
break down while sailing. The second difficulty will con- 
sist in the necessity for obtaining high initial velocities, 
so that the sustaining pressures shall be great, and that 
the dimensions and weight of the apparatus may conse- 
quently be reduced to a minimum. This difficulty of 
getting under way is the principal one encountered by 
birds, and probably furnishes the reason why none of 
them have attained the size of land and marine animals. 

It has been pointed out that there are no flying birds 
much over 30 lbs. in weight, and, reasoning from analogy, 
it has been argued that man cannot hope to improve upon 
nature in this direction ; but not only are birds much 
more complicated in structure than a flying machine needs 
to be, having many functions to perform such as wing- 
folding, feeding, reproduction, etc, besides that of mere 
flight, but they evidently expend much more energy in 
starting than in any other portion of their evolutions. 

The smaller ones jump from the ground into the air 
with all their might, and then beat their wings with much 
greater rapidity and amplitude than in their normal flight. 
If rising vertically they soon exhibit signs of distress. 
The larger birds in starting from the ground are com- 
pelled to run considerable distances, always against the 
wind, in order to gather headway and supporting power, 
and even with the most energetic flapping they cannot rise 
at a steeper angle than 45 . All birds prefer to start from 
a perch, for by directing their first course downward they 
gather velocity from the action of gravity ; at times some 
of the larger ones obtain relative velocity by simply 
spreading their wings wide open to the breeze while yet 
on the perch, the object in every case being to avoid the 
great exertion required to obtain speed, for once fairly 
under way they are masters of their movements. 

Resort to some equivalent devices will evidently be open 
to flying machines, but it is evident that until the question 
of stability has been thoroughly worked out, such experi- 
ments will be exceedingly dangerous ; no such apparatus 
has yet succeeded in raising itself from the ground with 
the whole of its motive power, and the most that can be 
said at present is that recent elucidations of the laws of 



35 

flight seem to indicate that it is not impossible for man to 
succeed with an aeroplane. 

There are probably scores of shapes which can be made 
available for such machines, just as there are hundreds of 
forms of birds who display various peculiarities in their 
flight ; but in every case there will be the same require- 
ments as to a light motor, absolute automatic stability and 
some device for gaining initial velocity, as well as for 
landing safely. This will require much experimenting, 
and a beginning has scarcely been made, so that even 
granting the accomplishment possible, the working out of 
the problem may prove to be slow. 

Success might be much hastened, however, by a work- 
ing association of searchers in this field of inquiry, for no 
one man is likely to be simultaneously an inventor, to 
imagine new shapes and new motors ; a mechanical engi- 
neer, to design the arrangement of the apparatus ; a mathe- 
matician, to calculate its strength and stresses ; a practical 
mechanic, to construct the parts, and a syndicate of capi- 
talists, to furnish the needed funds. It is probably because 
the working out of a complex invention requires so great 
a variety of talent, that progress in other fields has proved 
so slow, several generations sometimes passing before an 
important invention such as that of the steam-engine, the 
telegraph, or the reaping machine is finally perfected and 
brought into general use. 

CONCLUSION.* 

To sum up, therefore, the present " State of the Art" — 
if it has yet progressed sufficiently to be called an art — 
may be stated as follows : 

A measurable success has been attained with navigable 
balloons. They have been driven 14 miles per hour, and 
it is probable that speeds of 25 to 30 miles an hour, or 
enough to go out when the wind blows less than a brisk 
gale, are even now in sight. Very much more speed than 
this is not likely to be obtained with balloons, for lack of 
sufficiently light motive power, and because of unmanage- 
able sizes. 

Much greater speeds can perhaps be attained eventually 



* I have refrained in this paper from discussion of the various mathematical 
formulas concerning air resistances, because not only are they a matter of con- 
troversy, which must hereafter be settled by experiment, but also because the 
figures of M. Drzeweiki, which are based on empirical formulae, may be in 
need of revision ; for the benefit of the curious in such matters, however, it 
may be stated that his paper can be obtained (in French) in V A e)-onaute for Oc- 
tober, 1889. 



36 

with aeroplanes ; recent investigations indicate this ; but 
even a beginning is prevented by the lack of a light 
motor, and by questions as to the stability of the appa- 
ratus as well as to safe ways of gaining high initial veloc- 
ities. Whether these difficulties will ever be overcome 
no one knows, but they indicate the direction for investi- 
gation and experiment, while the probable benefits to man 
of a solution of the problem are so great that they are 
well worth striving for. 

Success with aeroplanes, if it comes at all, is likely to 
be promoted by the navigable balloon. It now seems not 
improbable that the course of development will consist, 
first, in improvements of the balloon, so as to enable it to 
stem the winds most usually prevailing, and then in using 
it to obtain the initial velocities required to float aero- 
planes. Once the stability of the latter is well demon- 
strated, perhaps the gas-bag can be dispensed with alto- 
gether, and self-starting, self-landing machines substi- 
tuted, which shall sail faster than any balloon ever can. 

If we are to judge of the future by the past, such im- 
provements are likely to be won by successive stages, each 
fresh inventor adding something to what has been accom- 
plished before ; but still, when once a partial success is 
attained, it is likely to attract so much attention that it is 
not impossible that improvements will follow each other 
so rapidly that some of the present generation will yet 
see men safely traveling through and on the air at speeds 
of 50 or 60 miles per hour. 



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